Transmit power adaptation algorithm using 802.11H

ABSTRACT

A first wireless device includes a signal strength module and a control module. The signal strength module is configured to receive a signal from a second wireless device, wherein the signal includes transmit power data indicating a transmit power of the second wireless device, and estimate a signal strength of the signal. The control module is configured to estimate a path loss between the first wireless device and the second wireless device based on (i) the signal strength and (ii) the transmit power data, and generate a control signal to control a transmit power of the first wireless device based on (i) the path loss and (ii) a sensitivity of a receiver of the first wireless device, where the sensitivity of the receiver is a minimum signal strength that the receiver is able to detect.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/400,982, filed Apr. 10, 2006, which claims the benefit of U.S.Provisional Application No. 60/738,693, filed Nov. 21, 2005. Thedisclosures of the above applications are incorporated herein byreference. This application is related to “BSS Selection Using PathLoss”, U.S. patent application Ser. No. 11/401,392 (now U.S. Pat. No.7,672,282), filed Apr. 10, 2006, which is hereby incorporated byreference in its entirety.

FIELD

The present disclosure relates to wireless network devices.

BACKGROUND

A wireless local area network (WLAN) provides a wireless station (STA),such as a laptop computer and/or networked appliance, with a wirelessconnection to a computer network. The STA includes a WLAN transceiverthat sends and receives packets. An access point (AP) also includes aWLAN transceiver that sends and receives the packets and provides acommunication bridge between the STA and the computer network.

In some instances more than one AP is available for providing the STAwith access to the computer network. The STA must then decide which APto associate with. Since many STAs are portable and powered bybatteries, it is prudent for the STA to consider battery life whenchoosing between the available APs. In some systems the STA monitors areceived signal strength indicator (RSSI) associated with signalsreceived from each of the APs. The STA then associates with the APhaving the strongest RSSI. This approach assumes that the RSSI providesan indication of the distance and/or proximity of the STA to the AP. TheSTA then assumes it can have a better quality communication path (e.g.lower signal loss and/or higher signal-to-noise ratio) with the APhaving the highest RSSI. Under this assumption the STA would conservebattery power by not having to resend packets that are dropped.

Referring now to FIG. 1, a functional block diagram is shown of a WLAN10. WLAN 10 includes a STA 12 that employs the RSSI approach describedabove. STA 12 can connect to a distributed communications system (DCS)14 such as the Internet through one of a first AP 16-1 and a second AP16-2. The first AP 16-1 may be located 100 meters from STA 12 and have aradiated power of 10 decibels over 1 milliwatt (10 dB_(m)). The secondAP 16-2 may be located 200 meters from STA 12 and have a radiated powerof 18 dB_(m).

Assuming free space propagation, the relation between RSSI in dB_(m)(Rx) and transmitted power in dB_(m) (Tx) at 5 Ghz, can be expressed as:Rx(D)=Tx−46.42−20 log D,  (Eq. 1)where D represents the distance in meters between the transmitter andthe receiver. The number 46.42 is a correction factor on the free-spacepath loss and is based on known equations and factors such as thefrequency of interest, conductor losses, and anticipated antenna gains.

As is shown below, Eq. 1 can be used to determine Rx values between STA12 and each of first AP 16-1 and second AP 16-2.Rx _(AP1)=10dB_(m)−46.42−20 log 100m=−76.42dB_(m), andRx _(AP2)=18dB_(m)−46.42−20 log 200m=−74.44dB_(m).Since Rx_(AP2)>Rx_(AP1), STA 12 will generate a stronger RSSI for secondAP 16-2. STA 12 will therefore associate with second AP 16-2 even thoughsecond AP 16-2 is further from STA 12 than first AP 16-1. This meansthat STA 12 will consume more power transmitting to second AP 16-2 thanit would have consumed transmitting to first AP 16-1.

SUMMARY

A wireless client station includes a received signal strength modulethat receives a signal from a wireless device and that estimates asignal strength of the signal. The signal includes transmit power data.A transmitter control module estimates a path loss to the wirelessdevice based on the signal strength and the transmit power data andgenerates a transmit power control signal based on the path loss.

In other features the wireless client station includes a transmitterthat generates a radio frequency signal having a power determined by thetransmit power control signal. The transmitter control module estimatesthe path loss further based on a link margin included in the signal. Thetransmitter control module updates the transmit power control signalwhen the path loss changes by a predetermined amount. The transmittercontrol module generates the transmit power control signal further basedon a predetermined transmit power delta. The wireless device includes anaccess point (AP). The wireless device includes a wireless clientstation. The signal is otherwise compliant with the Institute ofElectrical and Electronics Engineers (IEEE) standard 802.11H.

A wireless client station includes a received signal strength modulethat estimates N signal strengths of N packets received from N wirelessstations (STAs). The N packets include N corresponding transmit powervalues. A transmitter control module estimates N corresponding pathlosses to the N STAs based on the N signal strengths and N transmitpower values and generates a transmit power control signal based on theN path losses.

In other features the wireless client station includes a transmitterthat generates a radio frequency signal having a power determined by thetransmit power control signal. The transmitter control module estimatesthe N path losses further based on N link margins transmitted bycorresponding ones of the N STAs. The transmit power control signalincludes N magnitudes corresponding to the N path losses and thetransmitter control module updates one of the N magnitudes when acorresponding one of the N path losses changes by a predeterminedamount. The transmitter control module generates the transmit powercontrol signal further based on a predetermined transmit power delta.The N STAs are configured as an ad-hoc network. A magnitude of thetransmit power control signal is constant for all of the N path lossesand is based on one of the N path losses. The one of the N path lossescorresponds to a greatest one of the N path losses. The N packets areotherwise compliant with the Institute of Electrical and ElectronicsEngineers (IEEE) standard 802.11H.

A method of operating a wireless client station includes receiving asignal that includes transmit power data from a wireless device,estimating a signal strength of the signal, estimating a path loss tothe wireless device based on the signal strength and the transmit powerdata, and generating a transmit power control signal based on the pathloss.

In other features the method includes generating a radio frequencysignal having a power based on the transmit power control signal. Themethod includes estimating the path loss further based on a link marginincluded in the signal. The method includes updating the transmit powercontrol signal when the path loss changes by a predetermined amount. Themethod includes generating the transmit power control signal furtherbased on a predetermined transmit power delta. The signal is otherwisecompliant with the Institute of Electrical and Electronics Engineers(IEEE) standard 802.11H.

A method of operating a wireless client station includes estimating Nsignal strengths of N packets received from N wireless stations (STAs).The N packets include N corresponding transmit power values. The methodalso includes estimating N corresponding path losses to the N STAs basedon the N signal strengths and N transmit power values and generating atransmit power control signal based on the N path losses.

In other features the method includes generating a radio frequencysignal having a power determined by the transmit power control signal.The method includes estimating the N path losses further based on N linkmargins transmitted by corresponding ones of the N STAs. The transmitpower control signal includes N magnitudes corresponding to the N pathlosses. The method includes updating one of the N magnitudes when acorresponding one of the N path losses changes by a predeterminedamount. The method includes generating the transmit power control signalfurther based on a predetermined transmit power delta. The N STAs areconfigured as an ad-hoc network. A magnitude of the transmit powercontrol signal is constant for all of the N path losses and is based onone of the N path losses. The one of the N path losses corresponds to agreatest one of the N path losses. The N packets are otherwise compliantwith the Institute of Electrical and Electronics Engineers (IEEE)standard 802.11.

A method of operating a wireless client station includes estimating Nsignal strengths of N packets received from N wireless stations (STAs).The N packets include N corresponding transmit power values. The methodalso includes estimating N corresponding path losses to the N STAs basedon the N signal strengths and N transmit power values and generating atransmit power control signal based on the N path losses.

In other features the method includes generating a radio frequencysignal having a power determined by the transmit power control signal.The method includes estimating the N path losses further based on N linkmargins transmitted by corresponding ones of the N STAs. The transmitpower control signal includes N magnitudes corresponding to the N pathlosses. The method includes updating one of the N magnitudes when acorresponding one of the N path losses changes by a predeterminedamount. The method includes generating the transmit power control signalfurther based on a predetermined transmit power delta. The N STAs areconfigured as an ad-hoc network. A magnitude of the transmit powercontrol signal is constant for all of the N path losses and is based onone of the N path losses. The one of the N path losses corresponds to agreatest one of the N path losses. The N packets are otherwise compliantwith the Institute of Electrical and Electronics Engineers (IEEE)standard 802.11H.

A computer program stored on a tangible computer medium for operating awireless client station includes estimating N signal strengths of Npackets received from N wireless stations (STAs). The N packets includeN corresponding transmit power values. The computer program alsoincludes estimating N corresponding path losses to the N STAs based onthe N signal strengths and N transmit power values and generating atransmit power control signal based on the N path losses.

In other features, the computer program includes generating a radiofrequency signal having a power determined by the transmit power controlsignal. The computer program includes estimating the N path lossesfurther based on N link margins transmitted by corresponding ones of theN STAs. The transmit power control signal includes N magnitudescorresponding to the N path losses. The computer program includesupdating one of the N magnitudes when a corresponding one of the N pathlosses changes by a predetermined amount. The computer program includesgenerating the transmit power control signal further based on apredetermined transmit power delta. The N STAs are configured as anad-hoc network. A magnitude of the transmit power control signal isconstant for all of the N path losses and is based on one of the N pathlosses. The one of the N path losses corresponds to a greatest one ofthe N path losses.

A wireless client station includes received signal strength means forreceiving a signal from a wireless device and estimating a signalstrength of the signal. The signal includes transmit power data. Thewireless clients station also includes transmitter control means forestimating a path loss to the wireless device based on the signalstrength and the transmit power data and generating a transmit powercontrol signal based on the path loss.

In other features the wireless client station includes transmitter meansfor generating a radio frequency signal having a power determined by thetransmit power control signal. The transmitter control means estimatesthe path loss further based on a link margin included in the signal. Thetransmitter control means updates the transmit power control signal whenthe path loss changes by a predetermined amount. The transmitter controlmeans generates the transmit power control signal further based on apredetermined transmit power delta. The wireless device includes accesspoint (AP) means for providing a wireless connection to a distributedcommunications network. The wireless device includes client stationmeans for generating the signal. The signal is otherwise compliant withthe Institute of Electrical and Electronics Engineers (IEEE) standard802.11H.

A wireless client station includes received signal strength means forestimating N signal strengths of N packets received from N wirelessstations (STAs). The N packets include N corresponding transmit powervalues. The wireless client station also includes transmitter controlmeans for estimating N corresponding path losses to the N STAs based onthe N signal strengths and N transmit power values and generating atransmit power control signal based on the N path losses.

In other features the wireless client station includes transmitter meansfor generating a radio frequency signal having a power determined by thetransmit power control signal. The transmitter control means estimatesthe N path losses further based on N link margins transmitted bycorresponding ones of the N STAs. The transmit power control signalincludes N magnitudes corresponding to the N path losses and thetransmitter control means updates one of the N magnitudes when acorresponding one of the N path losses changes by a predeterminedamount. The transmitter control means generates the transmit powercontrol signal further based on a predetermined transmit power delta.The N STAs are configured as an ad-hoc network. A magnitude of thetransmit power control signal is constant for all of the N path lossesand is based on one of the N path losses. The one of the N path lossescorresponds to a greatest one of the N path losses. N packets areotherwise compliant with the Institute of Electrical and ElectronicsEngineers (IEEE) standard 802.11H.

In still other features, the systems and methods described above areimplemented by a computer program executed by one or more processors.The computer program can reside on a computer readable medium such asbut not limited to memory, non-volatile data storage and/or othersuitable tangible storage mediums.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the disclosure, are intended forpurposes of illustration only and are not intended to limit the scope ofthe disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a functional block diagram of a WLAN of the prior art;

FIG. 2 is a functional block diagram of a WLAN STA;

FIG. 3 is functional block diagram of a WLAN that includes the STA ofFIG. 2;

FIG. 4 is a protocol diagram of messages related to transmit power;

FIG. 5 is a flowchart of a method for choosing an AP to associate with;

FIG. 6 is a flowchart of a method for determining a minimum transmitpower;

FIG. 7 is a memory map of an array of minimum transmit power values;

FIG. 8 is a functional block diagram of a STA that includes anapplication program interface (API);

FIG. 9A is a table of API message fields in a transmit power controlconfiguration message;

FIG. 9B is a table of API message fields in a transmit power controlconfiguration response;

FIG. 10A is a functional block diagram of a high definition television;

FIG. 10B is a functional block diagram of a vehicle control system;

FIG. 10C is a functional block diagram of a cellular phone;

FIG. 10D is a functional block diagram of a set top box; and

FIG. 10E is a functional block diagram of a media player.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is in no wayintended to limit the disclosure, its application, or uses. For purposesof clarity, the same reference numbers will be used in the drawings toidentify similar elements. As used herein, the term module, circuitand/or device refers to an Application Specific Integrated Circuit(ASIC), an electronic circuit, a processor (shared, dedicated, or group)and memory that execute one or more software or firmware programs, acombinational logic circuit, and/or other suitable components thatprovide the described functionality. As used herein, the phrase at leastone of A, B, and C should be construed to mean a logical (A or B or C),using a non-exclusive logical or. It should be understood that stepswithin a method may be executed in different order without altering theprinciples of the present disclosure.

Referring now to FIG. 2, a STA 20 communicates with a host 22. By way ofnon-limiting example, host 22 can be implemented in a laptop computer,personal digital assistant, voice-over-internet protocol (VoIP)telephone, and/or other devices that communicate in a WLAN.

An interface 28 provides a communication bridge between host 22 and amedia access controller (MAC) 30. MAC 30 forms data from host 22 intopackets and communicates the packets to a modulator 32. MAC 30 alsoextracts data from packets that it receives from a demodulator 34. MAC30 communicates the extracted data to host 22 via interface 28.

MAC 30 includes a central processing unit (CPU) 36 and associated memory38. In addition to performing the data and packet operations describedabove, CPU 36 executes computer instructions that associate STA 20 withone of several access points (APs) 102 (shown in FIG. 3). CPU 36 alsoexecutes computer instructions that control a transmit power signal 40.

A transmit portion of STA 20 includes modulator 32 which digitallymodulates the packets and communicates them to a digital-to-analogconverter (D/A) 46. D/A 46 generates an analog modulating signal that iscommunicated to an RF transmitter 48. RF transmitter 48 generates one ormore modulated RF carriers based on the analog signal and applies themodulated RF carrier(s) to one pole of a digitally-controlled switch 51.A common terminal of switch 51 communicates with a feed line 50 thatconnects to an antenna (not shown). The RF transmitter and RF receiverform part of a physical layer (PHY) module 49 of the STA 20.

A receive portion of STA 20 receives modulated RF carrier(s) from theantenna through a second pole of switch 51. These modulated RFcarrier(s) are transmitted by APs 102 (see FIG. 3) and/or other STAs.The other STAs can be configured differently than STA 20. The modulatedRF carrier(s) are communicated to a receiver 62. Receiver 62 generates amodulated signal based on data included in the received modulated RFcarrier(s). An amplitude of the modulated signal is based on a gaincontrol signal 65 that is generated by a gain controller 81. Themodulated signal is communicated to an analog-to-digital converter (A/D)66 that generates modulated digital data based on the modulated signal.The modulated digital data is filtered by a low-pass filter 68 beforebeing communicated to an input of demodulator 34. Demodulator 34generates packets based on the filtered and modulated digital data andcommunicates the packets to MAC 30.

Demodulator 34 also generates a gain signal 70 based on the output oflow-pass filter 68. An error amplifier 72 generates an error signal 74based on a difference between gain signal 70 and a desired gain signal76 that is generated by MAC 30. An amplifier 78 amplifies the errorsignal 74 and communicates an amplified error signal to an accumulator80. Accumulator 80 integrates and/or differentiates the amplified errorsignal and generates an accumulated error signal that is communicated toan input of gain controller 81. Gain controller 81 then generates thegain control signal 65 and an RSSI signal 82 based on the accumulatederror signal.

Referring now to FIG. 3, a functional block diagram is shown of a WLAN100 that includes improved STA 20. STA 20 can connect to DCS 14 throughone of a first AP 102-1 and a second AP 102-2, collectively referred toas APs 102. Each of APs 102 are compliant with a transmit power control(TPC) protocol. The TPC protocol includes data regarding the RF powerbeing dissipated by the transmitting station. The data can be includedin a beacon signal and/or a response to a TPC request from another STA20.

Referring briefly to FIG. 4, a protocol diagram shows two methods thatSTA 20 and APs 102 use to implement the TPC protocol. The second of thetwo methods also allows APs 102 to transmit respective link margin datato STA 20. The link margins correspond to the communication pathsbetween the APs 102 and STA 20.

In the first method, AP 102 broadcasts a beacon message that includes atransmit power control (TPC) report 130. TPC report 130 includes thetransmitter RF power data of the transmitting AP 102.

In the second method, STA 20 sends a TPC request 132 to one of the APs102. The TPC request 132 includes the transmitter RF power data of STA20. Each AP 102 responds to TPC request 132 by sending a TPC reply 134.TPC reply 134 includes the transmitter RF power data of the sending AP102 and also a link margin between STA 20 and the sending AP 102. Insome embodiments TPC report 130, TPC request 132, and TPC reply 134,collectively referred to as TPC messages, are compliant with theInstitute of Electrical and Electronics Engineers (IEEE) 802.11hspecification, which is hereby incorporated by reference in itsentirety.

Returning now to FIG. 3, STA 20 uses the RF power data in the TPC report130 and/or TPC reply 134 to determine respective path losses in thecommunication paths between STA 20 and APs 102. STA 20 then associateswith the AP 102 that has the lowest path loss.

Path loss (PL) in dBm can be determined from the equation:PL=Tx−Rx,  (Eq. 2)where Tx is the RF power in dBm at the transmitter and Rx is based onthe received power as indicated by RSSI signal 82. Eq. 2 can beimplemented as computer instructions in memory 38 and executed by CPU36.

Example path loss calculations will now be provided that include thevalues shown in FIG. 3. Assuming APs 102-1 and 102-2 are transmitting 10dB_(m) and 18 dB_(m) of RF power respectively, then Eq. 1 shows thatRSSI signal 82 indicates Rx=−76.42 dB_(m) for first AP 102-1 andRx=−74.44 dBm for second AP 102-2. The path losses between STA 20 andAPs 62 can then be determined from Eq. 2 as follows:P _(LAP1)=10dB_(m)−(−76.42dB_(m))=86.42dB_(m) andP _(LAP2)=18dB_(m)−(−74.44dB_(m))=92.44dB_(m).For simplicity, small scale effects and multi-path fading are not takeninto account in the analysis above. The affect of distance becomes morepronounced when fading is taken into account. A similar conclusion canbe reached at in presence of multipath fading.

Referring now to FIG. 5, a method 120 is shown for determining which ofseveral APs 102 that STA 20 should associate with. Method 120 can beimplemented as computer instructions stored in memory 38 and executed byCPU 36. Method 120 can be executed each time STA 20 receives a TPCreport 130 and/or TPC reply 134.

Method 120 enters through block 122 and proceeds to block 124. In block124, control determines respective path losses between STA 20 and APs102 that transmit TPC reports 130 and/or TPC replies 134. Control thenproceeds to block 126 and associates STA 20 with the available AP 102corresponding to the lowest path loss. Control then proceeds to block127 and transmits a TPC request 132 (shown in FIG. 4). In response toTPC request 132, the associated AP 102 sends a TPC reply 134 thatincludes a Link Margin. Link Margin is described below. Control thenproceeds to block 128 and uses transmit power signal 40 to adjusttransmitter RF power to at least a minimum value Tx_(min) based on thecalculated path loss. Control then returns to other tasks via returnblock 129.

In block 128 control can determine Tx_(min) according to the followingproperties and equations. RF power losses in the communication path canbe described by:PL=TxPwr−RSSI  (Eq. 3)where PL is the path loss, in dBm, that corresponds with TPC reply 134,TxPwr is the transmitter RF power indicated in TPC reply 134, and RSSIis indicated the receive signal strength indication corresponding to themessage.

The link margin in the communication path can be described by:Link Margin=RSSI_(TPCReq) −Rx Sensitivity,  (Eq. 4)where Link Margin is expressed in dBm, RSSI_(TPCReq) is a receivedsignal strength indication at AP 102 (or another STA in an ad-hocnetwork) that corresponds to TPC request 132, and Rx Sensitivity is aminimum signal strength that receiver 62 is able to detect anddemodulate with a desired degree of reliability.

Assuming a symmetric link, control can determine Rx Sensitivity basedon:Rx Sensitivity=TxREQ−Path Loss−Link Margin,  (Eq. 5)where TxREQ is the transmitter RF power of STA 20. Control can thendetermine the minimum transmit power based onTx _(min) =PL+Rx Sensitivity  (Eq. 6)Control use the transmit power signal 40 to control the transmit powerbased on Tx_(min). In some embodiments the actual transmit power isdetermined based on a sum of Tx_(min) and a predetermined transmit powerdelta that is described below in more detail.

For a time varying channel or in a mobile environment, Path Loss will bea function of time. STA 20 can therefore execute a method, which isdescribed below, to adapt Tx_(min) according to changes in Path Loss.

Referring now to FIG. 6, a method 150 is shown for adjusting the minimumtransmitter power Tx_(min) of STA 20. Method 150 allows STA 20 toperiodically adapt Tx_(min) to changes in the path loss between STA 20and the associated AP 102. Changes in path loss are commonly caused bySTA 20 moving about within a coverage area of the associated AP 102. Asthe distance between the associated AP 102 and STA 20 reduces STA 20 canconserve energy by reducing Tx_(min). As the distance between theassociated AP 102 and STA 20 increases STA 20 can increase Tx_(min) aslittle as possible to maintain reliable communication with theassociated AP 102. Method 150 can be implemented as computerinstructions in memory 38 and executed by CPU 36. Method 150 can beexecuted each time STA 20 receives a TPC reply 134 and/or beacon 130.

Method 150 enters through block 152 and proceeds to decision block 154.In decision block 154, control determines an absolute value of thedifference between the present path loss (PathLoss_(t)) and the pathloss associated with the present value of Tx_(min) (PathLoss_(t0)).Control compares the absolute value to a predetermined path loss deltaΔ_(PathLoss). If the absolute value is larger than Δ_(PathLoss) thencontrol branches to block 156 and determines a new value of Tx_(min)based on the present path loss. On the other hand, if the absolute valueis less than Δ_(PathLoss) in decision block 154 then control branches toblock 158 and continues using the present value of Tx_(min). Controlreturns to other processes through return block 160 after completing thesteps of blocks 156 and 158.

Referring now to FIG. 7 a memory map 170 is shown of an array ofTx_(min) values. Such an array can be used when STA 20 is part of anad-hoc network. An ad-hoc network consists of a plurality of STAs anddoes not include an AP 102. The plurality of STAs communicate only witheach other and do not have access to DCS 14.

CPU 36 maintains memory map 170 in memory 38. Memory map 170 allocatesmemory for an identifier associated with each STA in the ad-hoc network.An example of an identifier includes a unique MAC address 172. Memorymap 170 also allocates memory for a Tx_(min) value associated with eachidentifier. In order for STA 20 calculate Tx_(min) the other STA mustuse the TPC protocol. STA 20 can use a default value of TX_(min) foreach STA that does not transmit the RF power data. STA 20 can adjust itstransmit power each time it transmits a data frame to a recipient STA.The transmit power is based on the Tx_(min) value associated with therecipient STA.

If STA 20 is not configured to modify transmit power on a per-framebasis then STA 20 can repeatedly use the transmit power corresponding tothe maximum of the Tx_(min) values computed for each of the STAs. Statedmathematically,Tx _(min)=max{Tx _(min1) ,Tx _(min2) , . . . , Tx _(minN)}  (Eq. 7)

Referring now to FIG. 8, a functional block diagram is shown of STA 20wherein host 22 includes a laptop computer. Host 22 includes a CPU (notshown) that communicates with CPU 36 via interface 28. CPU 36 supportsan application program interface (API) that is implemented in memory 38.The API provides a standard communication format for the values usedand/or determined in the methods described above.

Referring now to FIG. 9A various messages of the API are shown in tableform. The table of FIG. 9A shows command messages that host 22 sends toCPU 36. The table of FIG. 9B shows response messages that CPU 36 sendsto host 22. With the exception of a Result field at row 216, theresponse messages of FIG. 9B are an echo of the command messages of FIG.9A.

First column 201 indicates the name of each message. A second column 202indicates a data type for each message. Data type “UINT16” indicates anunsigned 16-bit integer and data type “UINT8” indicates an unsigned8-bit integer. Other data types can also be used to encode the messagedata. A third column 203 provides a description of each message.

The messages will now be described beginning with the top row 213.CmdCode is a fixed value that identifies the beginning of the APImessages of FIG. 9A. At row 214, Size indicates a number of bytes in theAPI messages of FIG. 9A. At row 215, SeqNum provides a serial number foreach transmitted group of API message. At row 216, Result is not usedwhen host 22 sends the API messages to CPU 36. CPU 36 populates theResult field when CPU 36 sends the API results (FIG. 9B) to host 22.

Examples of operations that have an effect on the Result field will nowbe described. At row 217, Action indicates whether host 22 desires toenable or disable one or both of methods 120 and 150. At row 218,Transmit Power Delta indicates an additional amount of power that STA 20desires to add to Tx_(min). The additional power provides a margin forerror when determining the path loss and Tx_(min). At row 219, Path LossTrigger Threshold indicates Δ_(PathLoss) that is used in block 154 ofmethod 150. CPU 36 populates the Result field with an indication ofwhether it successfully executed the Action, Transmit Power Delta,and/or Path Loss Trigger Threshold commands from host 22.

Referring now to FIGS. 10A-10E, various exemplary implementations of thepresent invention are shown.

Referring now to FIG. 10A, the present invention can be implemented in ahigh definition television (HDTV) 420. The present invention may beimplemented in a WLAN interface 429. The HDTV 420 receives HDTV inputsignals in either a wired or wireless format and generates HDTV outputsignals for a display 426. In some implementations, signal processingcircuit and/or control circuit 422 and/or other circuits (not shown) ofthe HDTV 420 may process data, perform coding and/or encryption, performcalculations, format data and/or perform any other type of HDTVprocessing that may be required.

The HDTV 420 may communicate with mass data storage 427 that stores datain a nonvolatile manner such as optical and/or magnetic storage devices.Mass data storage 427 can include at least one hard disc drive (HDD)and/or at least one optical digital versatile disc (DVD). The HDD may bea mini HDD that includes one or more platters having a diameter that issmaller than approximately 1.8″. The HDTV 420 may be connected to memory428 such as RAM, ROM, low latency nonvolatile memory such as flashmemory and/or other suitable electronic data storage. The HDTV 420 alsomay support connections with a WLAN via WLAN network interface 429. HDTV420 can include a power supply 423.

Referring now to FIG. 10B, the present invention may be implemented in aWLAN interface 448 of a vehicle 430. Vehicle 430 can include apowertrain control system 432 that receives inputs from one or moresensors 436 such as temperature sensors, pressure sensors, rotationalsensors, airflow sensors and/or any other suitable sensors and/or thatgenerates one or more output control signals 438 such as engineoperating parameters, transmission operating parameters, and/or othercontrol signals.

The present invention may also be implemented in other control systems440 of the vehicle 430. The control system 440 may likewise receivesignals from input sensors 442 and/or output control signals to one ormore output devices 444. In some implementations, the control system 440may be part of an anti-lock braking system (ABS), a navigation system, atelematics system, a vehicle telematics system, a lane departure system,an adaptive cruise control system, a vehicle entertainment system suchas a stereo, DVD, compact disc and the like. Still other implementationsare contemplated.

The powertrain control system 432 may communicate with mass data storage446 that stores data in a nonvolatile manner. Mass data storage 446 caninclude at least one HDD and/or at least one DVD. The HDD may be a miniHDD that includes one or more platters having a diameter that is smallerthan approximately 1.8″. The powertrain control system 432 may beconnected to memory 447 such as RAM, ROM, low latency nonvolatile memorysuch as flash memory and/or other suitable electronic data storage. Thepowertrain control system 432 also may support connections with a WLANvia WLAN network interface 448. The control system 440 may also includemass data storage, memory and/or a WLAN interface (all not shown). Thevehicle 420 can also include a power supply 433.

Referring now to FIG. 10C, the present invention can be implemented in acellular phone 450 that may include a cellular antenna 451. The presentinvention may be implemented in a WLAN interface 468. In someimplementations, the cellular phone 450 includes a microphone 456, anaudio output 458 such as a speaker and/or audio output jack, a display460 and/or an input device 462 such as a keypad, pointing device, voiceactuation and/or other input device. The signal processing and/orcontrol circuits 452 and/or other circuits (not shown) in the cellularphone 450 may process data, perform coding and/or encryption, performcalculations, format data and/or perform other cellular phone functions.

The cellular phone 450 may communicate with mass data storage 464 thatstores data in a nonvolatile manner. Mass data storage 464 can includeat least one HDD and/or at least one DVD. The HDD may be a mini HDD thatincludes one or more platters having a diameter that is smaller thanapproximately 1.8″. The cellular phone 450 may be connected to memory466 such as RAM, ROM, low latency nonvolatile memory such as flashmemory and/or other suitable electronic data storage. The cellular phone450 also may support connections with a WLAN via WLAN network interface468. The cellular phone 450 also may also include a power supply 453.

Referring now to FIG. 10D, the present invention can be implemented in aset top box 480. The present invention may be implemented in a WLANinterface 496. The set top box 480 receives signals from a source suchas a broadband source and outputs standard and/or high definitionaudio/video signals suitable for a display 488 such as a televisionand/or monitor and/or other video and/or audio output devices. Thesignal processing and/or control circuits 484 and/or other circuits (notshown) of the set top box 480 may process data, perform coding and/orencryption, perform calculations, format data and/or perform any otherset top box function.

The set top box 480 may communicate with mass data storage 490 thatstores data in a nonvolatile manner. Mass data storage 490 can includeat least one hard disc drive (HDD) and/or at least one optical digitalversatile disc (DVD). The HDD may be a mini HDD that includes one ormore platters having a diameter that is smaller than approximately 1.8″.The set top box 480 may be connected to memory 494 such as RAM, ROM, lowlatency nonvolatile memory such as flash memory and/or other suitableelectronic data storage. The set top box 480 also may supportconnections with a WLAN via WLAN network interface 496. Set top box 480can include a power supply 483.

Referring now to FIG. 10E, the present invention can be implemented in amedia player 500. The present invention may be implemented in a WLANinterface 516. In some implementations, the media player 500 includes adisplay 507 and/or a user input 508 such as a keypad, touchpad and thelike. In some implementations, the media player 500 may employ agraphical user interface (GUI) that typically employs menus, drop downmenus, icons and/or a point-and-click interface via the display 507and/or user input 508. The media player 500 further includes an audiooutput 509 such as a speaker and/or audio output jack. The signalprocessing and/or control circuits 504 and/or other circuits (not shown)of the media player 500 may process data, perform coding and/orencryption, perform calculations, format data and/or perform any othermedia player function.

The media player 500 may communicate with mass data storage 510 thatstores data such as compressed audio and/or video content in anonvolatile manner. In some implementations, the compressed audio filesinclude files that are compliant with MP3 format or other suitablecompressed audio and/or video formats. Mass data storage 510 can includeat least one hard disc drive (HDD) and/or at least one optical digitalversatile disc (DVD). The HDD may be a mini HDD that includes one ormore platters having a diameter that is smaller than approximately 1.8″.The media player 500 may be connected to memory 514 such as RAM, ROM,low latency nonvolatile memory such as flash memory and/or othersuitable electronic data storage. The media player 500 also may supportconnections with a WLAN via WLAN network interface 516. Media player 500can include a power supply 513. Still other implementations in additionto those described above are contemplated.

1. A first wireless device comprising: a signal strength moduleconfigured to receive a signal from a second wireless device, whereinthe signal received from the second wireless device includes transmitpower data indicating a transmit power of the second wireless device,and estimate a signal strength of the signal received from the secondwireless device; and a control module configured to estimate a path lossbetween the first wireless device and the second wireless device basedon (i) the signal strength of the signal received from the secondwireless device and (ii) the transmit power data indicating the transmitpower of the second wireless device, and generate a control signal tocontrol a transmit power of the first wireless device based on (i) thepath loss between the first wireless device and the second wirelessdevice and (ii) a sensitivity of a receiver of the first wirelessdevice, wherein the sensitivity of the receiver is a minimum signalstrength that the receiver is able to detect.
 2. The first wirelessdevice of claim 1, wherein: the signal received from the second wirelessdevice further includes a link margin corresponding to a communicationpath between the first wireless device and the second wireless device,and wherein the link margin is based on (i) a signal strength of asignal received at the second wireless device and (ii) the sensitivityof the receiver of the first wireless device.
 3. The first wirelessdevice of claim 2, wherein: the sensitivity of the receiver is based onthe transmit power of the first wireless device, the path loss betweenthe first wireless device and the second wireless device, and the linkmargin corresponding to the communication path between first wirelessdevice and the second wireless device.
 4. The first wireless device ofclaim 1, further comprising a transmitter configured to: generate aradio frequency (RF) signal having a power determined by the controlsignal, and transmit the RF signal having the power determined by thecontrol signal to the second wireless device.
 5. The first wirelessdevice of claim 1, wherein: the first wireless device is a clientstation; and the second wireless device is an access point or a clientstation.
 6. A wireless device, comprising: a signal strength moduleconfigured to receive N signals from N wireless devices, respectively,where N is an integer greater than or equal to 1, wherein the N signalsinclude N transmit powers indicating transmit powers of the N wirelessdevices, respectively, and estimate N signal strengths of the N signalsreceived from the N wireless devices, respectively; and a control moduleconfigured to estimate N path losses between the wireless device and theN wireless devices, respectively, determine that the wireless device isto associate with one of the N wireless devices having a lowest of the Npath losses, and generate a control signal to control a transmit powerof the wireless device based on (i) the lowest of the N path losses and(ii) a sensitivity of a receiver of the wireless device, wherein thesensitivity of the receiver is a minimum signal strength that thereceiver is able to detect.
 7. The wireless device of claim 6, wherein aP^(th) of the N path losses is based on (i) a P^(th) of the N signalstrengths and (ii) a P^(th) of the N transmit powers indicating atransmit power of the P^(th) of the N wireless devices, where P is aninteger, and 1≦P≦N.
 8. The wireless device of claim 6, furthercomprising a transmitter configured to: generate a radio frequency (RF)signal having a power determined by the control signal, and transmit theRF signal having the power determined by the control signal to the oneof the N wireless devices having a lowest of the N path losses.
 9. Thewireless device of claim 6, wherein: the wireless device is a clientstation; and at least one of the N wireless devices is an access pointor a client station.
 10. The wireless device of claim 9, wherein thecontrol module is further configured to set the transmit power of thewireless device to a highest of transmit powers of the N wirelessdevices.
 11. A method for a first wireless device, the methodcomprising: receiving a signal from a second wireless device, whereinthe signal received from the second wireless device includes transmitpower data indicating a transmit power of the second wireless device;estimating a signal strength of the signal received from the secondwireless device; estimating a path loss between the first wirelessdevice and the second wireless device based on (i) the signal strengthof the signal received from the second wireless device and (ii) thetransmit power data indicating the transmit power of the second wirelessdevice; and generating a control signal to control a transmit power ofthe first wireless device based on (i) the path loss between the firstwireless device and the second wireless device and (ii) a sensitivity ofa receiver of the first wireless device, wherein the sensitivity of thereceiver is a minimum signal strength that the receiver is able todetect.
 12. The method of claim 11, wherein: the signal received fromthe second wireless device further includes a link margin correspondingto a communication path between first wireless device and the secondwireless device, and wherein the link margin is based on (i) a signalstrength of a signal received at the second wireless device and (ii) thesensitivity of the receiver of the first wireless device.
 13. The methodof claim 12, wherein: the sensitivity of the receiver is based on thetransmit power of the first wireless device, the path loss between thefirst wireless device and the second wireless device, and the linkmargin corresponding to the communication path between first wirelessdevice and the second wireless device.
 14. The method of claim 11,further comprising: generating a radio frequency (RF) signal having apower determined by the control signal, and transmitting the RF signalhaving the power determined by the control signal to the second wirelessdevice.
 15. The method of claim 11, wherein: the first wireless deviceis a client station; and the second wireless device is an access pointor a client station.
 16. A method for a wireless device, the methodcomprising: receiving N signals from N wireless devices, respectively,where N is an integer greater than or equal to 1, wherein the N signalsinclude N transmit powers indicating transmit powers of the N wirelessdevices, respectively, and estimating N signal strengths of the Nsignals received from the N wireless devices, respectively; estimating Npath losses between the wireless device and the N wireless devices,respectively; determining that the wireless device is to associate withone of the N wireless devices having a lowest of the N path losses; andgenerating a control signal to control a transmit power of the wirelessdevice based on (i) the lowest of the N path losses and (ii) asensitivity of a receiver of the wireless device, wherein thesensitivity of the receiver is a minimum signal strength that thereceiver is able to detect.
 17. The method of claim 16, wherein a P^(th)of the N path losses is based on (i) a P^(th) of the N signal strengthsand (ii) a P^(th) of the N transmit powers indicating a transmit powerof the P^(th) of the N wireless devices, where P is an integer, and1≦P≦N.
 18. The method of claim 16, further comprising: generating aradio frequency (RF) signal having a power determined by the controlsignal, and transmitting the RF signal having the power determined bythe control signal to the one of the N wireless devices having a lowestof the N path losses.
 19. The method of claim 16, wherein: the wirelessdevice is a client station; and at least one of the N wireless devicesis an access point or a client station.
 20. The method of claim 19,further comprising setting the transmit power of the of the wirelessdevice to a highest of transmit powers of the N wireless devices.